In general, carboxylic amide compounds are known as useful intermediates for cationic surfactants of quaternary ammonium salts and amphoteric surfactants of a betaine type. Also, carboxylic amide itself is used for hair rinses, hair conditioners and the like as an amine salt.
Qualities required to such carboxylic amides and derivatives thereof such as quaternary ammonium salts, betaine and amine salts include a good color tone and a good odor.
Usually, the above carboxylic amide compounds can be produced by subjecting fatty acids or esters thereof and diamine to dehydration and condensation. In general, this condensation reaction proceeds by reacting higher fatty acids or esters thereof with diamine at a reaction temperature of 80 to 200° C. under atmospheric pressure or reduced pressure. Usually, a small amount of impurities present in the raw materials is converted to colored substances by heat or in the presence of a trace amount of air to cause a marked degradation in the color and the odor, and a large effect is exerted on a color tone and an odor of the products and a color tone and an odor of the finished products.
In general, carboxylic amide having a long chain alkyl group has a high melting point and is solid at room temperature, and therefore it is stored in a liquid state under heating or it is stored in the form of a solid matter and has to be molten by heating before producing derivatives such as quaternary ammonium salts and betaine.
However, carboxylic amide causes a deterioration in a color tone by being subjected to heat history to result in exerting an adverse effect on the qualities of the products such as quaternary ammonium salts and betaine.
An improvement in a color tone by adding (10 to 1000 ppm), for example, VIII group metal compounds such as sodium boron hydride (NaBH4) has so far been known as a method for improving a color tone of carboxylic amide and derivatives thereof (refer to, for example, patent documents 1 and 2).
However, in the methods described in these documents, the color tone is not sufficiently improved by a lower limit value (10 ppm) prescribed in the claims, and when the addition amount is increased to 100 ppm or more, the compounds are not dissolved in carboxylic amide to generate precipitates. Further, when the compounds are added in an amount of 1000 ppm and the products are stored under heating, the problem that the base material is decomposed is brought about.
Also, sodium borohydride is a water-prohibiting substance and has the problem that it is difficult to handle in terms of safety since it generates hydrogen in treating.
Patent document 1: Japanese Patent Application Laid-Open No. 253446/1996 (claims, page 3 to page 4 and the like)
Patent document 2: Japanese Patent Application Laid-Open No. 235260/1997 (claims, page 3, examples and the like)